Rotatable coupler



Aug.26,1947. LABIN ETAL 2,426,226

ROTATABLE GOUPLER Filed Jan. 25, 1943 ATLI'IJRALEYy Patented Aug. 26, 1947 4 2,426,226 ROTATABLE COUPLER Emile Labin and Armig G. Kandoian, New York, N. Y., assignors to Federal Telephone and Radio Corporation, Newark, N. J., a corporation of Delaware Application January 23, 1943, Serial No. 473,311

1 Claim. 1 This invention relates to rotatable couplers and more particularly to rotatable coupler arrangements for interconnecting coaxial lines.

It is often desirable to provide for rotatable coupling in transmission lines, particularly for rotatable antennas, goniometers or the like. Rotatable couplers are generally made with rubbing contacts between the stationary and movable parts. Such contacts tend to introduce disturbances due to Variations and contact pressure upon rotation of the element.

Other types of rotatable couplers such as the usual condenser or inductance arrangements are not generally suitable for wide band frequency transfer since they are generally quite critical to a particular frequency and do not smoothly pass other frequencies but tend to introduce considerable disturbance in the line.

It is a principal object of our invention to provide a rotatable coupler free from the objections of these previously known rotatable couplers.

It is a further object of our invention to provide a rotatable coupler which will serve to transfer energy between a iixed and a rotatable line portion over a relatively wide frequency band without introducing substantial disturbance tending to upset the impedance matching of the line.

In accordance with a feature of our invention, we provide a rotatable coupling device between coaxial transmission lines by expanding the relatiVe diameters of the inner and outer conductors at the end of each line over a length in the order of a quarter of a wavelength at the operating frequency band and arrange these expanded portions to nest together so that the desired coupling is obtained.

A better understanding of our invention and the objects and features thereof may be had from the description of a particular example thereof made with reference 'to the accompanying drawing, in which:

Fig. 1 is a perspective view partly lbroken away of a rotatable coupler in accordance with our invention; Y

Fig. 2 is a schematic diagram of a rotatable coupler such as shown in Fig. 1; and

Fig. 3 is a modified form of the coupler arrangement of Fig. 2.

Turning to Fig. 1 the rotatable coupler is shown applied to couple together translator l which may be a radio transmitter or receiver and a rotatable antenna or goniorneter Il. From translator l0 extends a coaxial line l and axially therewith extends a coaxial line 2 from antenna Il.

The inner conductor of coaxial line l extends beyond the end of the normal outer conductor as shown at 3.

The inner conductor of coaxial Yline 2 is expanded as shown at 4 and extends around extended conductor 3. As illustrated, conductor 4 is made the same diameter as coaxial lines I and 2. Other diametral dimensions may be used for this expanded line as desired. Furthermore, if portion yl is expanded to a Wider diameter, the portion of inner conductor 3 may also be expanded as desired.

The outer conductor of line l is expanded to a larger diameter as'shown at 5 and the outer conductor of line 2 is also expanded as shown at 6 and extends outside the cylindrical portion 5 of line l. All of these expanded portions 4 to 6, inclusive, are made approximately a quarter of a wavelength long at the mid-frequency of the band at which the circuit is designed to operate. The ends of the various portions are brought close to one another as shown in the drawing but are retained in spaced relationship.

Since the expanded portions of the coupler -are made substantially a quarter of a wavelength long, they introduce into the line very little disturbance and at the mid-frequency of theband may introduce no disturbance so that the line remains matched in spite of the coupling unit. At this mid-frequency substantially no currents are induced in the outer surface of the coaxial line conductors but at the frequencies removed from the mid-frequency some currents tend to be induced in the outer conductor of line I. Accordingly, we provide a shield 'l approximately a quarter of a wavelength long. This shield is in the form of a cylinder open at one end, this open end extending up to or a slight ways between the extended portions A5 and 6 of the outer conductors and at its closed end is fastened directly to the outer surface of the outer conductor of' coaxial line I. The shielding cylinder l need not extend inside portion `6 as shown. The essential structure merely requires that the open end of cylinder 1 extend to a point beyond the open end of the portion 6.

The rotatable coupler may be readily supported on the translating unit l0 in the manner illustrated. Flanged support 8 is mounted directly on the translator panel. At the upper end of cylinder 8 is provided a bearing support 9 with which cooperates the bearing member l2 fixed to the outer surface of portion E. The antenna is thus supported for rotation on this rotatable mount. Although a simple friction bearing is shown by -ductor -of line l.

. 3 way of example, it is clear that any desired type of bearing such as thrust roller bearings or ball bearings could be used to make rotation easier. Since there are substantially no currents in the outer conductor 6, the bearings may be mounted any place along this outer conductor.

Fig. 2 illustrates more clearly the relative arrangement of the various parts of Fig. 1 in a simplied diagrammatic showing.

In Figs. 1 and 2 the inner and outer conductors of the transmission lines I and 2 are shown interleaved at the rotating cable coupling element. The arrangement of these conductors may be altered, if desired, so that the elements are not interleaved as illustrated in Fig. 3. In this arrangement the inner conductor of line I is expanded as shown at 23 so that it extends about the outer surface of an extended portion of inner conductor 24 of line 2. The outer conductor of line 2 is then expanded so that it is directly outside of the expanded portion 25 of the outer con- It is clear that other modifications of the arrangement as to the spacing of the conductors may be provided and the input and output ends of the circuit may be interchanged Without-materially affecting the operation of the system.

We have found that this rotatable coupling unit provides a system which will carry a wide band of frequencies without introducing serious disturbance in the lines at ultra high frequencies. In a particular model a coupling was arranged for agiven frequency. In this arrangement lines I and Z were made of standard 7A; inch coaxial line. Portion 6 Was made 5 inches in diameter while portion was made 3 inches in diameter. -With this arrangement the system was found to introduce no missmatch between the lines at the given frequency for which it Was designed and introduced less than a 2-to-1 standing wave disturbance in the transmission line over a band Aextending a given 130 megacycles each side of the vNumber inder such as shown at 1, Figs. 1 and 2, may be provided with the arrangement shown in Fig. 3 as well.

While we have described above the principles of our invention in connection with specific apparatus, and particular modications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention as set forth in the objects of our invention and the accompanying claim.

What is claimed is:

A rotatable coupler for intercoupling coaxial transmission lines, comprising a hollow cylindrical extension open at one end fixed to the central conductor of one of said transmission lines at its closed end, said extension being in the order of a quarter wavelength long at the operating frequency, the inner conductor of the other of said transmission lines extending coaxially into the open end of said cylinder, extended cylindrical portions on the corresponding ends of the outer conductors of said coaxial transmission lines, said portions being of different diameters from the extended inner conductor and each other, and of substantially a quarter wavelength long, said portions being coaxially mounted with respect to one another and said hollow cylinder extension, whereby transfer of energy between said sections at said operating frequency may be accomplished by electromagnetic coupling and further comprising a cylindrical conductor structure in the order of a quarter wavelength long fastened at one end'to the outer surface of one of said outer conductors, the other end thereof extending a small distance into the opening between said cylindrical portions, whereby currents induoed in the outer surface of 'said one outer conductor are substantially suppressed.

EMILE LABIN. ARMIG G. KANDOIAN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Name Date 2,401,344 Espley June 4, 1946 

